Invoice numbering rules under GST
Sixteen characters, one unbroken series per financial year, never reused.
Last checked 20 September 2026
A GST invoice number can be at most 16 characters, using letters, digits, hyphens and slashes. It must be unique within the financial year and come from a consecutive series. Numbers restart each financial year, and once a number is issued it is never reused.
The rules
| Rule | Detail |
|---|---|
| Length | Maximum 16 characters |
| Characters | Letters, digits, hyphen (-) and slash (/). Nothing else |
| Uniqueness | Unique for that financial year within your business |
| Sequence | Consecutive — a series, not arbitrary numbers |
| Reset | The series starts again each financial year, from 1 April |
A format that works
The rules do not prescribe a format, only the constraints. A pattern most businesses land on is a short prefix, the financial year, and a padded serial:
| Part | Example | Why |
|---|---|---|
| Prefix | MPK | Identifies your business, or a branch, or a series |
| Financial year | 25-26 | Makes the year unmistakable on a filed copy |
| Serial | 00001 | Padded, so numbers sort correctly everywhere |
Giving MPK/25-26/00001 — fifteen characters, inside the limit, with room to grow to 99,999 invoices a year.
Count your characters before you commit
A long branch code plus a year plus a six-digit serial overruns 16 characters easily, and you will not find out until an e-invoice or a return is rejected. Count once, at the start of the year.
More than one series
You may run several series — per branch, per counter, per document type — as long as each is itself consecutive and every number is unique across the business for the year. Distinguish them in the prefix, for example MPK/25-26/00001 for tax invoices and MPK-RI/25-26/00001 for retail bills.
Credit notes and debit notes carry their own numbers under the same constraints.
Gaps, and why they are a problem
The series is meant to be consecutive. A gap invites the obvious question — what was invoice 47, and why is it not here? There may be a perfectly good answer, but you have to be able to give it.
- Cancelled before issue: keep the cancelled number on record, marked cancelled, rather than pretending it never existed.
- Wrong after issue: do not delete it. Issue a credit note against it.
- Deleted by accident: the number stays gone. Note what happened, when, and why.
Never reuse a number
Reissuing a number that has been used — especially one already reported in a return — creates two different documents with the same identity. That is far worse than a gap.
Why this should be automatic
Everything above is exactly the kind of rule software should enforce rather than a person remember: issue the next number at the moment of generation, never let two people take the same one, never allow it to be typed by hand, and roll the year over without being asked. That is how invoice numbering works in TracEasy.
Can I include the month in the number?
Yes, within 16 characters, as long as the series is still consecutive. Most businesses find the year is enough and the month just eats characters.
Can I start at 1000 instead of 1?
Yes. What matters is that it is consecutive from wherever it starts.
I changed software mid-year. Do I restart?
You do not have to, and continuing the existing series is usually cleaner. Just do not produce duplicates of numbers already issued.
Sources
- CGST Rules 2017, Rule 46 — particulars of a tax invoice
- CBIC — GST Acts, Rules and notifications (cbic-gst.gov.in)